(1) Field of the Invention
The present invention relates to a feedstuff for swine and, more specifically, relates to a feedstuff for swine containing an additional amount of L-tryptophan or its salt, in addition to a required amount of L-tryptophan, together with the other essential constituents.
(2) Description of the Prior Art
Feedstuffs for swine are generally divided into those for suckling pigs, those for pigs including yound gilts, young boars, and adult sires, those for breeding swines or sows, and those for lactating sows, depending upon their ages and usage. Raw materials and guaranteed amounts of ingredients are decided upon so that the feedstuffs are most desirably adapted for the desired purposes, taking into consideration the required nutrients, feed efficiencies, economic factors, and other factors.
As essential (or indispensable) amino acids for swine, the following ten (or twelve) amino acids are known: L-arginine, L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-threonine, L-tryptophan, and L-valine (and L-cystine, and L-tyrosine). All these essential amino acids should be present in the required amounts in the feedstuffs. The required amounts of the essential amino acids are set forth in NRC (National Research Council) Requirements or Japanese Feeding Standard. These standard requirements depend upon the kinds of swines. It is well-known in the art that, if the content of a certain amino acid is less than the required amount, the effectively available amounts of the other essential amino acids are limited to the level of said certain amino acid. This means that the extra amounts of said other essential amino acids are wastefully consumed. Such an amino acid is called a first-limiting amino acid. The kind of the limiting amino acid depends upon the sources of feedstuffs. It is reported, for example, that lysine is the first-limiting amino acid and tryptophan is the "second-limiting" amino acid in milo and corn. On the other hand, tryptophan is the first-limiting amino acid in fishmeals and methionine is the first-limiting amino acid in soybean meal.
The above-mentioned amino acids are contained in the form of protein in the feedstuffs. The feedstuffs are generally prepared from, for example, corn and milo as a carbohydrate source and soybean meal and fishmeals as a protein source. Commercially available feedstuffs for swine generally contain about 0.15% to 0.25% by weight of tryptophan component as a protein-constituting amino acid, although this tryptophan content largely depends upon the breeding or growing period of swines. This tryptophan content sufficiently satisfies that of nutrient requirements growing swine set forth in the Japanese Feeding Standard issued in 1975 (i.e., 0.11% to 0.18% by weight). According to the prior studies, the effective availability of tryptophan contained as a protein in the feedstuffs is about 50% to about 80% of free tryptophan (i.e., tryptophan not in the form of the constituent of protein). The tryptophan content in the commercially available feedstuffs is determined by multiplying the tryptophan requirement by the effective availability of tryptophan. It has been believed that the further addition of tryptophan to the feedstuffs does not have any significant effects on, for example, increases in milk yields and body weight of dams, an increase in growth rate of farrows, a reduction of recurrence days of estrus, and an increase in the body weight gain of fattening pigs or hogs.